Heat transfer systems



Dec. 20, 1960 w. B. HALL HEAT TRANSFER SYSTEMS 2 Sheets-Sheet 1 Filed Sept. 27, 1957 WILLIAM BATEMAN HALL Invent Attorneys Dec. 20, 1960 w. B. HALL 2,965,555

HEAT TRANSFER SYSTEMS Filed Sept. 27, 1957 2 SheetsSheet 2 WILLIAM BAflEMAN HALL Attorneys United States Patent HEAT TRANSFER SYSTEMS William Bateman Hall, Seascale, Cumberland, England, assignor to United Kingdom Atomic Energy Authority, London, England Filed Sept. 27, 1957, Ser. No. 686,639

Claims priority, application Great Britain Sept. 28, 1956 6 Claims. (Cl. 204-1932) This invention relates to heat transfer systems and is concerned primarily with extended heat transfer surfaces associated with fuel elements for nuclear reactors.

The development of extended heat transfer surfaces for fuel elements started princip lly with longitudinally finning and later brought forth circumferential finning. In this latter arrangement the loss due to increased pumping power required to drive a coolant over the fuel elements was more than compensated for by improved heat transfer characteristics. It has been assumed that with circumferential finning (i.e., extended surfaces transverse to the main coolant flow), a toroidal vortex is set up between the fins which has the property of satisfactorily interchanging heat between the hot fuel element surface and the coolant gas. However, with the present development of nuclear reactors for generating vendible electricity there is a continual effort to reduce the temperature difference between the heat generting fuel element and coolant gas on emergence from the reactor and accordingly improved heat transfer surfaces on the fuel elements are sought after.

The present invention provides such improved heat transfer surfaces.

According to the invention a body having an array of fins transverse to the length of the body is ch-racterised in that at least one segment of each fin is deflected relative to the remaining segments of the fin in a direction along the axis of the body.

A preferred heat transfer system utilising a body according to the invention comprises a circular channel having axially located therein a circumferentially finned fuel element, the fins being divided into an even number of segments greater than two and the segments being alternately deflected against and with the direction of fluid flow along the channel. The fins may be radially cut to permit the deflection or merely counterdeflected with points of inflexion.

The invention will now be described with reference to the three part-sectional perspective views of the accompanying drawings identified as Figs. 1, 2 and 3, and the fragmentary view, Fig. 4.

In Fig. 1 an elementary fin 10 is shown in a channel 11 along which a coolant fluid flows in the direction of an arrow 12. The fin has a cut 13 in the proximity of the fin tip to make two segments 14, 15, the segment 14 of the fin being deflected against the direction of the arrow 12 and the segment 15 deflected with the direction of the arrow 12. The arrows 16, 17 are intended to suggest a mechanism whereby coolant is taken from the general stream by the segment 14 and urged back into the stream with the aid of the segment 15 so that the cooling process can be regarded as a main stream (the Patented Dec. 20, 1960 arrow 12) with a fraction continuously withdrawn to sweep the hot surface 18 at the root of the fin and then return to the stream. This mechanism could reasonably also occur with only segment 15 or segment 14 deflected, but to a less effective extent.

In Fig. 2 part of a fuel element 27 having a sheath 28 and circumferential fins 20 is shown in a circular section channel 21, along which coolant flows in the direction of an arrow 22. The fins 20 have four cuts 23 and are alternately curved, segments 24 of the fin being curved against the direction of the arrow 22 and segments 25 being curved with the direction of the arrow 22. A mechanism based on the creation of four vertices is suggested as indicated by the arrows and lines 26.

Fig. 3 shows an arrangement similar to Fig. 2 (the same reference numerals being used) only the cut 13 is replaced by inflexions 13a.

The curved fins may be formed by dropping the fuel element, whilst hot, so that the fins plastically deform, through a circular die with two opposed faces of increased curvature to form one pair of deflections and then lifting the element through a die having two pairs of opposed faces all of said incre:sed curvature to form the other pair of deflections.

In Fig. 4 a normally deflected fin 24 is shown together with coolant flow indicated by the arrow 22. It is found that improved heat transfer characteristics may be obtained if the tip 29 of the fin is trimmed as indicated by the line 30 so that the fin presents a cutting edge to the coolant flow 22.

I claim:

1. A body having an array of fins of constant radius transverse to the length of the body, said fins being divided into an even number of equal segments greater than two, the outer edges of the segments of each fin being deflected chord wise towards a direction parallel to the longitudinal axis of the body and each segment being deflected in the opposite direction to the adjacent segments on the respective fin.

2. A body according to claim 1 characterised in that the body is a nuclear reactor fuel element.

3. A body according to claim 1 characterised in that the fins are radially cut to permit the deflection.

4. A body according to claim 1 axially located in a channel for controlling the flow of a heat transfer fluid over the body.

5. A body according to claim 4 characterised in that the tips of the fins are trimmed so as to present a cutting edge to the flow of heat transfer fluid.

6. A body according to claim 1 wherein the segments are deflected in opposite directions with points of inflection between opposed deflections.

References Cited in the file of this patent UNITED STATES PATENTS 2,216,778 Houdry Oct. 8, 1940 2,217,469 Clarke Oct. 8, 1940 2,335,918 Davis et al. Dec. 7, 1943 2,418,619 Brown Apr. 8, 1947 2,454,357 Tolan Nov. 23, 1948 2,620,171 Dubin et a1 Dec. 2, 1952 OTHER REFERENCES Nucleonics, June 1955, vol. 13, No. 6, page 93. 

1. A BODY HAVING AN ARRAY OF FINS OF CONSTANT RADIUS TRANSVERSE TO THE LENGTH OF THE BODY, SAID FINS BEING DIVIDED INTO AN EVEN NUMBER OF EQUAL SEGMENTS GREATER THAN TWO, THE OUTER EDGES OF THE SEGMENTS OF EACH FIN BEING DEFLECTED CHORD WISE TOWARDS A DIRECTION PARALLEL TO THE LONGITUDINAL AXIS OF THE BODY AND EACH SEGMENT BEING DEFLECTED IN THE OPPOSITE DIRECTION TO THE ADJACENT SEGMENTS ON THE RESPECTIVE FIN.
 2. A BODY ACCORDING TO CLAIM 1 CHARACTERISED IN THAT THE BODY IS A NUCLEAR REACTOR FUEL ELEMENT. 